86 Bronco II - Hesitates, stumbles while accellerating

[brotherjeremiah]

Hello All,
I am new to the site(new to posting that is)and I have a 1986 BII 2.9.
I am experiencing similar issues to a lot of other BII owners, which is a misfire or hesitation while accelerating.
Background: Purchased about 2 mos ago, had brand new plugs, wires, distributor cap, rotor, rebuilt tranny, new waterpump...hopefully im not missing anything. 106, xxx miles, ran great for 1st month, no problems. Took it on an 80 mile trip and about 70 miles in, while accelerating, it felt like it just cut out, no power, wouldnt rev, finally got it up to speed but took a lot of babying the gas. Parked it for a good 4 hours when I got to my destination. Drove another 30 miles after that no problems at all. Problem returned on my return trip again about 50 miles in this time. So since this initial issue it has started to happen sooner and sooner once i begin driving, and now its to the point that it happens as soon as it warms up(about 5 min of driving). It starts off mild and gets more severe the longer it is driven. It idles fine, maybe like a very slight miss, no smoke from exhaust. Visually inspected vacuum lines-everything seems ok, replaced TFI as I suspected this was the most likely culprit.

So, it does not seem like a wiring issue or bad ground, i think those issues would be more sporadic, timing is correct, spark on all cylinders, etc., which leads me to believe the problem lies within a sensor for the fuel injection system, vacuum leak that worsens as vehicle heats up, gasket that may loosen when warm, so on...

Any ideas on where to start? Ive read every post on this site I could pertaining to the topic, and while several are similar, nothing seems to match my symptoms. I am pretty close to buying all new components -egr valve, solenoid, press feedback sens, collant temp sensor, air temp sensor, knock sensor, o2 sensor, map, and fuel pressure regulator. I would really like to put this moeny towards other upgrades on the vehicle so if anyone has advice I would greatly appreciate it.

 

[adsm08]

Change the oxygen sensor.

 

[brotherjeremiah]

Problem still occurs at WOT. From what I understand O2 sensor is bypassed when at WOT, correct?

 

[brotherjeremiah]

Another interesting thing I recently noticed, when i turn the key on(but not crank it) i can hear the HP fuel pump kick in but it does not turn off...shouldnt it prime the system and shut off after 2-5 secs...maybe this is part of the problem?

 

[adsm08]

It should prime and shut off, but if it is stuck full bore that isn't your problem. That's not really a huge problem in a return-type fuel system. Just make sure it is getting the full 12 volts.

Yes, the O2 is largely ignored at WOT. You may also have problems with the MAP sensor or the throttle position sensor.

Unplug the MAP, if it's working the engine will die. If it's the problem it will start to run a little better.

 

[sjr53]

The fuel pumps should shut off after 1-2 seconds. The computer should shut off the pump relay when it doesn't see any signal from the TFI indicating the engine is running. Checking the fuel pressure when it isn't running right would be the 1st thing I would do. I just had my LP pump in the tank fail. Fortunately it didn't completely die until I made it home. I cut a hole in the floor to get to it. What a rusty mess the electrical connections and fuel line stems from the tank were. $106 from O'Reilly's got me the new pump/sender assembly. My fuel gauge works now for the 1st time since I bought it 16 years ago. It used to show empty after 10 gallons were gone.

 

[brotherjeremiah]

I unplugged map while idling and rpms went up a bit then stabilized...seemed to end up running worse than normal but didnt shut off.

Should I try to drive it with the map unplugged? or does the fact that it still ran when it was unplugged mean i should replace it?



I checked resistance on the tps with ohmmeter while moving throttle - i dont recall the range but it did increase and decrease smoothly with throttle - but the connector looks a little rough - goal for the weekend is to try and locate a better looking harness from the local pick-n-pull.



I plan to borrow a pressure gauge this weekend to see if i notice a difference while problem occurs.

thanks

 

[brotherjeremiah]

So over the weekend I replaced MAP sensor, egr valve, egr vacuum solenoid, tps, and I found a Pressure Feedback Egr sensor at the pick and pull.

Still having the same problem. So i pulled the throttle body and new egr off and there was a carbon buildup about 1.5 inches tall and nearly sealed over around the port that connects the egr valve to the intake manifold. I cleaned the buildup off and made sure the port was clear with compressed air. Problem still there.

Previously I had 2 different people at an auto parts store check codes, and both times i was told there were no codes. Today I decided to try to run them myself with a test light, and this is what I got in the order they were displayed:

KOEO: 87 Fuel pump circuit fault

Memeory: 33 EGR did not open intermittently

KOER: 41 System lean - Fuel control

33 EGR did not open/ respond during test

25 Knock sensor not tested (ignore if not pinging)

74 Brake On Off (BOO) signal open or short to ground

So i guess the 33 and 41 are key. Would 33 cause 41, or vice versa?

Is there a way to test pfe sensor?(thats the only part I replaced that wasn't new) Tried www.fordfuelinjection.com but didnt find anything there

Anyone had a similar issue?

Thanks for any input!

 

[alwaysFlOoReD]

Have you checked your fuel pressure? Should be at 40 psi. Mine was at 20-22 and I was having the same symptoms as you. It ends up the PO used a fuel pump from a mustang when transplanting a 4.0 into my carbed '85 b-II and used a NON-fuel type hose connection inside the tank. I'm not saying that is the exact problem you have but checking the fuel pressure would eliminate fuel pressure from the equation, tho volume may still have some bearing, in which case replacing the filter/s should fix that. Like sjr53 said, cutting a hatch into the floor is the easiest route to access the pump.

Good luck,

Richard

 

[AK Bronco2]

This is the best thing I have ever Seen.....

Thanks alwaysFlOoReD

 

[b2legnick]

The fuel pumps should shut off after 1-2 seconds. The computer should shut off the pump relay when it doesn't see any signal from the TFI indicating the engine is running. Checking the fuel pressure when it isn't running right would be the 1st thing I would do. I just had my LP pump in the tank fail. Fortunately it didn't completely die until I made it home. I cut a hole in the floor to get to it. What a rusty mess the electrical connections and fuel line stems from the tank were. $106 from O'Reilly's got me the new pump/sender assembly. My fuel gauge works now for the 1st time since I bought it 16 years ago. It used to show empty after 10 gallons were gone.

my b2 does the exact same thing...when i first got it i looked it up and it had a 17g tank and i would fill it up and it would only hold 9/10 gal.

 

[b2legnick]

Hello All,
I am new to the site(new to posting that is)and I have a 1986 BII 2.9.
I am experiencing similar issues to a lot of other BII owners, which is a misfire or hesitation while accelerating.
Background: Purchased about 2 mos ago, had brand new plugs, wires, distributor cap, rotor, rebuilt tranny, new waterpump...hopefully im not missing anything. 106, xxx miles, ran great for 1st month, no problems. Took it on an 80 mile trip and about 70 miles in, while accelerating, it felt like it just cut out, no power, wouldnt rev, finally got it up to speed but took a lot of babying the gas. Parked it for a good 4 hours when I got to my destination. Drove another 30 miles after that no problems at all. Problem returned on my return trip again about 50 miles in this time. So since this initial issue it has started to happen sooner and sooner once i begin driving, and now its to the point that it happens as soon as it warms up(about 5 min of driving). It starts off mild and gets more severe the longer it is driven. It idles fine, maybe like a very slight miss, no smoke from exhaust. Visually inspected vacuum lines-everything seems ok, replaced TFI as I suspected this was the most likely culprit.

So, it does not seem like a wiring issue or bad ground, i think those issues would be more sporadic, timing is correct, spark on all cylinders, etc., which leads me to believe the problem lies within a sensor for the fuel injection system, vacuum leak that worsens as vehicle heats up, gasket that may loosen when warm, so on...

Any ideas on where to start? Ive read every post on this site I could pertaining to the topic, and while several are similar, nothing seems to match my symptoms. I am pretty close to buying all new components -egr valve, solenoid, press feedback sens, collant temp sensor, air temp sensor, knock sensor, o2 sensor, map, and fuel pressure regulator. I would really like to put this moeny towards other upgrades on the vehicle so if anyone has advice I would greatly appreciate it.

Ive been told my b2 has a damaged injector due to the fact that it had a rusty gas tank and was drove for awhile before new tank was installed...which causes it to be hard to start and tries to hop and sometimes no throttle response and will die randomly when it sits and idles. And mine dies instantly when i unplug the map sensor...hope something from this helps...